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Rice develops first method to sort nanotubes by size
June 26, 2006Method sorts nanotubes based on unique electric properties
HOUSTON — Rice University scientists have developed the first method for sorting semiconducting carbon nanotubes based on their size, a long-awaited development that could form the basis of a nanotube purification system capable of producing the necessary feedstocks for nano-circuits, therapeutic agents, next-generation power cables and more.
Nanotubes, tiny cylinders of carbon no wider than a strand of DNA, possess a tantalizing array of properties coveted by materials scientists. Nanotubes are stronger than steel, but weigh one sixth as much. Some varieties are excellent semiconductors, while others are metals that conduct electricity as well as copper.
But there are dozens of varieties of nanotubes, each slightly different in size and atomic structure and each with very different properties. For many applications, engineers need to use just one type of nanotube, but that's not possible today because all production methods turn out a mishmash of types.
New research due to appear in an upcoming issue of the Journal of the American Chemical Society describes a new method that uses electric fields to sort nanotubes by size.
"People have developed sorting methods based on both chemical and electrical properties, but ours is the first that's capable of sorting semiconducting nanotubes based upon their dielectric constant, which is determined by their diameter," said corresponding author, Howard Schmidt, executive director of Rice's Carbon Nanotechnology Laboratory (CNL).
To sort nanotubes, the CNL team built a system that capitalizes on the fact that each type of nanotube has a unique dielectric constant — a term that refers to a material's ability to store electrostatic energy. CNL scientists created an electrified chamber and pumped a solution of dissolved nanotubes through it. The chamber traps metallic nanotubes and causes semiconducting varieties to float at different levels in the chamber. The smaller the diameter of the nanotube, the larger the dielectric constant and the lower in the system the tubes float. By varying the speed of flow through the system — with upper-level currents traveling faster than lower-level currents — the scientists were able to collect samples that had three times more small tubes than large and vice versa.
Rice University
But there are dozens of varieties of nanotubes, each slightly different in size and atomic structure and each with very different properties. For many applications, engineers need to use just one type of nanotube, but that's not possible today because all production methods turn out a mishmash of types.
New research due to appear in an upcoming issue of the Journal of the American Chemical Society describes a new method that uses electric fields to sort nanotubes by size.
"People have developed sorting methods based on both chemical and electrical properties, but ours is the first that's capable of sorting semiconducting nanotubes based upon their dielectric constant, which is determined by their diameter," said corresponding author, Howard Schmidt, executive director of Rice's Carbon Nanotechnology Laboratory (CNL).
To sort nanotubes, the CNL team built a system that capitalizes on the fact that each type of nanotube has a unique dielectric constant — a term that refers to a material's ability to store electrostatic energy. CNL scientists created an electrified chamber and pumped a solution of dissolved nanotubes through it. The chamber traps metallic nanotubes and causes semiconducting varieties to float at different levels in the chamber. The smaller the diameter of the nanotube, the larger the dielectric constant and the lower in the system the tubes float. By varying the speed of flow through the system — with upper-level currents traveling faster than lower-level currents — the scientists were able to collect samples that had three times more small tubes than large and vice versa.
Rice University
Nanotubes News and Current Nanotubes Events RSSTrue properties of carbon nanotubes measured
For more than 15 years, carbon nanotubes (CNTs) have been the flagship material of nanotechnology. Researchers have conceived applications for nanotubes ranging from microelectronic devices to cancer therapy. Their atomic structure should, in theory, give them mechanical and electrical properties far superior to most common materials.
Slipping through cell walls, nanotubes deliver high-potency punch to cancer tumors in mice
The problem with using a shotgun to kill a housefly is that even if you get the pest, you'll likely do a lot of damage to your home in the process. Hence the value of the more surgical flyswatter.
Golden Scales: Nanoscale Mass Sensor from Berkeley Can Be Used to Weigh Individual Atoms and Molecules
There's a new "gold standard" in the sensitivity of weighing scales. Using the same technology with which they created the world's first fully functional nanotube radio, researchers with Berkeley Lab and the University of California (UC) at Berkeley have fashioned a nanoelectromechanical system (NEMS) that can function as a scale sensitive enough to measure the mass of a single atom of gold.
'Nanonet' circuits closer to making flexible electronics reality
Researchers have overcome a major obstacle in producing transistors from networks of carbon nanotubes, a technology that could make it possible to print circuits on plastic sheets for applications including flexible displays and an electronic skin to cover an entire aircraft to monitor crack formation.
Researchers generate hydrogen without the carbon footprint
A greener, less expensive method to produce hydrogen for fuel may eventually be possible with the help of water, solar energy and nanotube diodes that use the entire spectrum of the sun's energy, according to Penn State researchers.
LLNL researchers peer into water in carbon nanotubes
Researchers have identified a signature for water inside single-walled carbon nanotubes, helping them understand how water is structured and how it moves within these tiny channels.
The fight for the best quantum bit (qubit)
Our results give us, for the first time, the possibility to understand the interaction between just two electrons placed next to each other in a carbon nanotube.
Perfecting a solar cell by adding imperfections
Nanotechnology is paving the way toward improved solar cells. New research shows that a film of carbon nanotubes may be able to replace two of the layers normally used in a solar cell, with improved performance at a lower cost. Researchers have found a surprising way to give the nanotubes the properties they need: add defects.
Secret ingredient: nanoparticles aid bone growth
In the first study of its kind, bioengineers and bioscientists at Rice University and Radboud University in Nijmegen, Netherlands, have shown they can grow denser bone tissue by sprinkling stick-like nanoparticles throughout the porous material used to pattern the bone.
NASA Scientists Pioneer Method for Making Giant Lunar Telescopes
Scientists working at NASA's Goddard Space Flight Center in Greenbelt, Md., have concocted an innovative recipe for giant telescope mirrors on the Moon. To make a mirror that dwarfs anything on Earth, just take a little bit of carbon, throw in some epoxy, and add lots of lunar dust.
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